1. Field of the Invention
Embodiments of the present invention generally relate to a method and apparatus for enhancing image or video quality using an exposure aware scene adaptive global brightness contrast.
2. Description of the Related Art
Global Brightness Contrast Enhancement (GBCE) is an important component in a digital camera that improves brightness and contrast of the image/video using adaptive tone mapping under various scene conditions. GBCE has become important in recent times due to the introduction of wide dynamic range sensors where the images are captured with the large dynamic range and a need exists to preserve the content in the both bright and dark regions. Rendering the optimal brightness and contrast improves overall image/video quality.
This is a challenging task since most often GBCE is adjusted based on the histogram alone. The global brightness enhancement (GBE) component increases the brightness by applying a gain to the histogram and the global contrast enhancement (GCE) component enhances the contrast by stretching the histogram and filling in the empty spaces in the histogram.
FIG. 1 is an embodiment of a tone mapping based on input histogram. This phenomenon is shown in FIG. 1, where a tone curve is shown based on a input histogram. As seen in FIG. 1, the curve has a positive slope (expansion) where the histogram bins are occupied and depicts a negative slope (compression) where the histogram bins are empty. The vertical lines show the shadow, mid tone and highlight regions.
Traditionally, the histogram does not fully represent the image content information and the image quality can be improved optimally if brightness and contrast can be adjusted based on image content information. A similar content of the image (e.g., sky, foliage, face) can be in shadow, mid tone or highlight regions, and the image needs to be tuned differently based on the scene condition. Some of the common problems that most existing GBCE algorithms encounter are that noise is amplified in dark/low light images, color gets de-saturated, mid-tones do not remain intact, highlight regions (e.g. bright light, snow regions) are over saturated, and the GBCE algorithm does not generalize well on a large image set.
Furthermore, sometimes the auto-exposure (AE) system can underexpose or overexpose the image due to poor metering and hence brightness of the image needs to be adjusted by the GBCE system and the information can be fed back to the AE system. Histogram Equalization (HE) is known to be one of the simplest techniques to improve brightness and contrast; however, most often the image looks washed out since it equalizes the histogram to a uniform distribution which is not optimal.
Since GBCE is the most important visual rendering component of the image besides color, this has to be adjusted optimally which means that the histogram needs to be controlled in an optimal manner such that all the content of the image is preserved. Therefore, there is a need for an improved method and/or apparatus for enhancing an exposure aware scene adaptive global brightness contrast.